FISHERY BULLETIN: VOL. 77. NO, 3 



Salinit\' and Temperature Kxperiment 



The effect of salinity on hatching of resting eggs 

 was reexamined (Figure 11) at lower tempera- 

 tures (15°, 12.5°, 10° C) which are marginal to 

 unfavorable for growth of the A. californiensis 

 population (Figures 2, .3). The basic intent was to 

 determine, if possible, the lowest termperature- 

 salinity combination(s) which could break dia- 

 pause of the overwintering eggs. 



General hatching patterns as a function of salin- 

 ity (Figure 11) were similar to those observed at 

 17° C (Figure 8) in that hatching rates decreased 

 with decreasing salinity at all three temperatures. 



Incubation Tinne (days) 



Figure ll. — Hatching rate and cumulative success of field- 

 collected resting eggs of Acar/ia spp. in various salinities at; (A) 

 15° C, (B) 12. .5" C, andiC) 10" C. Lower temperatures and salin- 

 ities increased to 1,5° C and 15%o, respectively, after variable 

 periods of incubation to determine short-term "holding" success 

 at suboptimal conditions. 



Lower temperatures similarly reduced hatching 

 rates and final hatches at a given salinity. How- 

 ever, the interactive effect of temperature with 

 salinity increased nonlinearly as temperature de- 

 creased (Figure 11). As a result, the percentage of 

 resting eggs remaining in a state of dormancy 

 became progressively larger with decreasing 

 temperature. 



Few Acartia spp. resting eggs incubated at 15° 

 or 12.5° C (Figure 11 A, B) failed to terminate dia- 

 pause and begin development. As observed at 17° 

 C, embrvogenesis progressed to the final prehatch 

 stage, apparently independent of external salin- 

 ity. Subsequent holding time (pseudodormancyi 

 depended on the interaction of salinity and 

 temperature. For example, hatching rates at 25"/oo, 

 15%o, and 10"/oo, while progressively reduced, were 

 still relatively high with very little dormancy evi- 

 dent. The majority of eggs hatched within 3-4 

 days. Final hatches were high and in a narrow 

 range from 91-81% at 15° C to 84-71% at 12.5° C. 

 However, some prehatch holding did occur at 

 these higher salinities since an increase in salin- 

 ity (107oii to 15%o; Figure 11 A) or temperature 

 (12.5° to 15° C; Figure IIB) resulted in an addi- 

 tional 5-9% hatch. 



Prehatch holding at 5%ii was increasingly more 

 important with decreasing temperature (Figure 

 11 A, B). At 15° C, the 5%o hatching rate was 

 greatly reduced, but was still substantial and 

 similar to that seen at 17° C (Figure 8). Over 50% 

 hatch was attained by day 7, with hatching con- 

 tinuing to 62% on day 15. Viability of the remain- 

 ing eggs (38% ) was low since a salinity increase to 

 25"/«« only yielded an additional 11% hatch. In 

 comparison, prehatch holding in b"U at 12.5° C 

 (Figure IIB) was pronounced since the hatching 

 rate was reduced to only 1-2% • day' . However, 

 the holding dormancy was only a temporary condi- 

 tion since hatching continued throughout the 

 15-day exposure to 5'W Viability was reduced but 

 still substantial as seen in a final hatch of 68% in 

 25%o. Thus, hatching in 5%.. water at 12.5° C or 15° 

 C would have probably continued until all eggs 

 either hatched or died from exhaustion of energy 

 reserves during the holding state. 



Hatching results at 10° C (Figure IIC) were 

 considerably different from results at 12.5° C and 

 15° C in that dormancy was a major factor at all 

 salinities. For example, final hatches (prior to 

 changes) at 25%o, 15'U, and 10%.. were 61% , 40%, 

 and 33%, respectively. This represented a 23-38% 

 increase in dormancy from that at 12.5° C. Persis- 



578 



